1. Field of the Invention
The present invention relates to a tandem type mass analysis system, and in particular, it relates to the differential analysis using a tandem type mass analysis system.
2. Description of the Related Art
The outline of the differential analysis using the tandem type mass analysis will be explained with reference to FIG. 1. According to the tandem type mass analysis, first, the mass analysis distribution of the substances contained in a specimen is measured. Thereby, the mass analysis spectra (MS1) of the first stage can be obtained. The horizontal axis of the mass analysis spectra denotes the ratio of the mass to the charge m/z, and the vertical axis the number of detected ions. Next, from the mass analysis spectra of the first stage (MS1), the ions are selected from the one having a higher number of detected ions. Here, the ions A, B, D are selected. The ions selected accordingly are referred to as precursor ions or parent ions. The parent ions are dissociated, and each of the dissociated ions is measured for the mass analysis distribution. Thereby, the mass analysis spectra of the second stage (MS2) can be obtained.
The mass analysis spectra (MS2) of the second stage are compared with the mass analysis spectra of the second stage (MS2) of standard specimens measured preliminarily. In the case there is a difference therebetween, the ion is judged to be a differential component of the specimen.
In the case comparison of the mass analysis spectra of the second stage is insufficient, the differential component may be determined by obtaining the mass analysis spectra of the third stage (MS3) and comparing the same with the mass analysis spectra of the standard specimen. Accordingly, by obtaining the mass analysis spectra of the multiple stages and comparing the same with the mass analysis spectra of the standard specimen, further accurate specimen differential analysis results can be obtained.
Accordingly, the tandem type mass analysis denotes the technique of repeating selection of the parent ions and dissociation of the same for carrying out the mass analysis.
For example, the mass analysis spectra (MS2) are measured preliminarily from a specimen derived from a healthy person and they are stored in a reference data base. By the comparison of the mass analysis spectra (MS2) obtained from a specimen derived from an examinee with the mass analysis spectra (MS2) of the healthy person, the differential component is detected. From the differential component detected accordingly, the health state of the examinee can be judged.
Japanese Patent Application Laid-Open Nos. 2001-249114 and 2001-330599 disclose an example of the differential analysis of comparing the mass analysis spectra obtained from a specimen derived from an examinee with the mass analysis spectra obtained from a specimen derived from a healthy person stored in a standard data base.
In the differential analysis using the tandem type mass analysis, for improving the detection accuracy of the differential component, a larger number of the selected parent ions is preferable. In the embodiment of FIG. 1, the ions A, B, D are selected as the parent ions without selecting the ion C. With the premise that the differential component was not detected as a result of comparison of the mass analysis spectra of the second stage mass analysis spectra of the ions A, B, D and the mass analysis spectra of the standard specimen, in this case, it is judged that the specimens as the analysis subjects do not have a differential component. However, a differential component may be detected by comparing the mass analysis spectra of the second stage of the ion C and the mass analysis spectra of the standard specimen.
If the number of the parent ions is increased, the process of measuring the mass analysis spectra of the second stage (MS2) is increased. In general, most of the components in the analysis subject specimens is included in the standard specimen. Therefore, most of the measurement process for the second mass analysis spectra (MS2) concerning the parent ions is wasted. With a larger number of the parent ions, the wasteful measurement process is increased accordingly.